The P 225 is the civilian version of the the German police service pistol P6. It was developped around the requirements for a police pistol back in its day. The P220 was too large.
The P1 is the old civilian Walther P 38,
# P1 - P38, Walther
# P2 - Sig 210
# P3 - 600/43, Astra
# P4 - shorter improved version of P1
# P5 - P5, Walther
# P6 - P225, Sig Sauer
# P7 - PSP, HK
# P8 - USP Variante, HK
# P9 - P99, Walther
# P10 - USP Compact, HK
# P11 - P11, HK
# P12 - USP Tactical .45, HK